FLT CREW OF SA227; CONFUSED BY ATCT LCL CTLR'S IDENT OF THEIR FLT NUMBER INCURRED ON RWY 34R AT SEA WHEN 1 PLT MISTOOK THE CLRNC TO HAVE BEEN GIVEN TO ANOTHER ACFT.

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AFTER LNDG ON RWY 34L AT SEATTLE TACOMA INTL; WE TAXIED OFF ONTO TXWY F AND WERE INSTRUCTED TO HOLD SHORT OF RWY 34R. OUR CALL SIGN WAS XXXAEA. SHORTLY THE CTLR CALLED WITH THE FOLLOWING INSTRUCTION: 'YYYAEA CROSS RWY 34R WITHOUT DELAY.' HEARING THE NUMBER 'AEA;' I STARTED THE ROLL. THE FO VERIFIED THAT THE XING INSTRUCTION WAS FOR US. THE TWR THEN INSTRUCTED US TO HOLD SHORT: 'XXXAEA HOLD SHORT OF RWY 34R.' I STOPPED IMMEDIATELY BUT HAD PASSED THE HOLD SHORT LINES BY ABOUT 20 FT BUT WAS STILL FAR FROM THE RWY EDGE LINES. THE TWR DID NOT SAY ANYTHING ELSE. AN AIRLINER LANDED ON RWY 34R; STOPPED WELL SHORT OF OUR INTXN; AND CLRED THE RWY. WE WERE THEN INSTRUCTED TO CROSS RWY 34R. THE PRIMARY CAUSE FOR THIS INCIDENT WAS THE CTLR CALLING US YYY INSTEAD OF XXX. I DID NOT HEAR ANY YYY FLT WITH THE SAME CALL SIGN WHILE ON THE APCH. IF THE FO HAD NOT VERIFIED THE INSTRUCTION WE WOULD HAVE CROSSED THE RWY BEFORE THE AIRLINER LANDED. HOWEVER THE BEST COURSE OF ACTION; WHICH WOULD CERTAINLY HAVE AVOIDED THIS INCIDENT; WOULD HAVE BEEN TO VERIFY THE XING INSTRUCTION BEFORE STARTING THE XING OF RWY 34R.